BACKGROUND:The COVID-19 pandemic resulted in the development and use of a plethora of SARS-CoV-2 serology assays, each reporting results in its own assay units, confounding attempts to compare results between different studies. In 2021, WHO commissioned the HARMONY study to calibrate some of the most widely used commercial SARS-CoV-2 spike protein-binding antibody assays relative to the first WHO International Standard for anti-SARS-CoV-2 immunoglobulin (National Institute for Biological Standards and Control [NIBSC] code 20/136) and assess the harmonisation of data. METHODS:Diagnostic test manufacturers participating in HARMONY were provided with three standard preparations: the first WHO International Standard, the NIBSC anti-SARS-CoV-2 Antibody Diagnostic Calibrant (code 20/162), and the US SARS-CoV-2 serology standard (Frederick National Laboratory for Cancer Research). The manufacturers followed a standardised study protocol to titrate their in-house reference (IHR) or calibrant and the three standards, performing each experiment in triplicate. Results were submitted for the centralised statistical analysis of dose-response curve data and calculation of potency estimates relative to the International Standard, expressed in binding antibody units per mL (BAU/mL). FINDINGS:14 manufacturers took part in the study, submitting results from 22 different test and target combinations. Each manufacturer's IHR material was successfully calibrated against the first WHO International Standard and assigned a unitage in BAU/mL relative to the International Standard. Quantification of IgG levels in BAU/mL for each secondary standard showed harmonisation of results for assays measuring binding to the same antigenic target (receptor binding domain [RBD], spike subunit 1 [S1], or spike). For the US serology standard, good agreement was observed for the three participating S1 IgG assays (geometric mean 739 BAU/mL [95% CI 617-885]; geometric coefficient of variation [GCV] 18%) and the six RBD IgG assays (701 BAU/mL [640-768]; GCV 12%). Similar concordance was observed for the NIBSC anti-SARS-CoV-2 Antibody Diagnostic Calibrant 20/162, with BAU/mL estimates for S1 IgG (2356 BAU/mL [2118-2620]; GCV 12%, n=3) and RBD IgG (2096 BAU/mL [1856-2368]; GCV 17%, n=6). INTERPRETATION:These findings provide proof-of-concept evidence that for the biologically important SARS-CoV-2 spike protein, levels of anti-RBD, S1, or spike IgG binding antibodies can successfully be compared across a range of well validated commercial assays with different designs and formats through previous calibration and reporting in standardised units. The BAU/mL values assigned to the two secondary standards enable their use as alternative calibration reagents. FUNDING:WHO and the Swiss Agency for Development and Cooperation.

Lassa fever is a zoonotic disease endemic to several West African countries, with seasonal outbreaks and potential to cause future epidemics. Vaccines and other medical countermeasures are in development, requiring reliable assays for evaluation. A WHO International Standard (IS) for anti-Lassa virus (LASV) antibodies can support harmonization of serological assay results, aiding vaccine and therapeutic assessment, surrogates of protection identification, and improving epidemiological understanding. In this study, a pooled plasma sample from Lassa fever survivors was evaluated in a multi-centre collaborative study involving 17 laboratories for its suitability as a reference material for detecting anti-LASV antibodies. Additionally, two well-characterized monoclonal antibody (mAb) cocktails were assessed as potential alternatives to convalescent plasma. Expressing the antibody titre of the collaborative study panel samples relative to the convalescent plasma pool (NIBSC 20/202) or the mAb cocktails harmonized the results from the participants reducing the inter-laboratory variation. However, while the candidate IS 20/202 performed consistently across all assays, the mAb cocktails were not detected by a few binding antibody methods. These findings support the use of mAb cocktails as reference material for evaluating humoral responses within a laboratory or network using common assays; however, for an IS, applicable globally across methods, convalescent serum or plasma remains the most suitable material.

Measurement of serum immunoglobulin G (IgG) to Shigella lipopolysaccharide (LPS) has been proposed as a correlate of protection against shigellosis, the confirmation of which in the target population of infants in low- and middle-income countries will facilitate vaccine development and licensure. Data obtained from Shigella sonnei vaccine clinical studies have identified a protective serum LPS IgG threshold value that is assay-specific. In the interim period before an International Standard serum was available, a retrospective bridging study using a panel of human serum samples had been conducted to estimate the anti-S. sonnei LPS IgG levels in two ELISA methods, employed in several ongoing or recently completed age-descending Shigella vaccine clinical studies that correspond to the threshold titer of 1,600 established using the Tel Aviv University ELISA method. Each lab performed its own in-house ELISA protocol and tested a panel of 32 human serum samples, covering a range of anti-S. sonnei LPS IgG levels. We observed excellent correlation of the ELISA data between the laboratories and used the fitted equations from regression analysis to determine the values that correspond to an endpoint titer of 1,600 in the Tel Aviv University ELISA method. Our analysis provides a way to meaningfully compare results obtained with clinical samples across the ELISA methods used by the three participating laboratories.IMPORTANCETo support large-scale efficacy trials, especially where efficacy trials are not feasible, the ability to compare immune response data across candidate Shigella vaccines can be very valuable for identifying the most promising vaccine platform and immunobridging to other populations, vaccine formulations, or additional platforms in the future. However, international standards for antibody assays are not yet available for Shigella vaccines currently in clinical development. Lack of standardization of Shigella immunoassays means that the results of antibody measurement in clinical samples from different vaccine trials or those from seroepidemiology studies cannot be easily compared. The results from this study will facilitate the comparison of immunological titers obtained across different Shigella vaccine studies as an interim measure until such time that immunoassays can be better harmonized through the use of an International Standard Serum.

Disclosure: K. Partridge: None. C. Sturgeon: None. E. Atkinson: None. M. Moore: None. P. Rigsby: None. B. Cowper: None. Alpha-fetoprotein (AFP) is a glycoprotein in the serum albumin family, primarily produced in the liver of foetuses during gestation. While AFP levels are normally low in the blood and serum of non-pregnant adults, levels increase during the first and second trimester of pregnancy. Higher than normal levels in pregnancy can also be indicators of birth defects such as anencephaly, omphalocele and spina bifida. Elevated levels in non-pregnant adults can also be indicative of disease, including hepatocellular carcinoma, germ cell tumours, and chronic active hepatitis. Measurement of AFP by immunoassays has therefore become widely established in the diagnosis and monitoring of disease states, responsiveness of patients to therapy, and in Triple and Quad pregnancy screening. Of the many commercially available AFP immunoassays on the market, the majority are traceable to the 1st WHO International Standard for Alpha Fetoprotein (1st WHO IS for AFP, 72/225), where it serves as a tool aimed at harmonisation of AFP immunoassay measurements. Stocks of the 1st WHO IS are now exhausted. Therefore, a replacement WHO IS, coded 22/216, has recently been produced at the MHRA. In this study, we describe the process of developing and characterising the 2nd WHO IS. With support from UKNEQAS, via an International Collaborative Study, we (i) evaluated the suitability of a highly purified preparation of AFP from human cord serum to serve as the 2nd WHO IS, (ii) value assigned the candidate standard, in international units (IU), in terms of the 1st WHO IS, by immunoassay, (iii) assessed commutability of the candidate standard with clinical samples in major commercial assays and (iv) evaluated long term stability of 22/216 by accelerated thermal degradation analysis. 20 different immunoassay platforms were used, including both manual and automated ELISA methods. Data from the study demonstrated good parallelism for the candidate IS, relative to the 1st WHO IS, indicating the candidate IS behaves in a similar manner to the current IS, allowing for the overall geometric mean potency value to be assigned as 7756 IU/ampoule (inter-lab GCV 8.73%). Commutability of candidate IS preparations with clinical samples was mixed, but comparable to those shown for the 1st WHO IS, 72/225, using a “calibration effectiveness” approach. Finally, accelerated thermal degradation samples were tested by immunoassay. Data indicated that 22/216 showed good stability with an estimated loss in potency of 0.07% per year when stored at -20°C Taken together, the data supports the introduction of 22/216 as the replacement IS for AFP, to continue to aid harmonisation of AFP immunoassays. 22/216 was established as the 2nd WHO IS by the WHOs Expert Committee on Biological Standardisation (ECBS), and replaces the 1st WHO IS, 72/225. Presentation: Monday, July 14, 2025

IntroductionRecent public health emergencies of international concern (PHEIC) have highlighted the need to develop prophylactic treatments and effective diagnostics for pandemic preparedness. In particular, the 100 Days Mission, an initiative to respond to a PHEIC within the first 100 days after declaration, has put into focus the importance of the early availability of effective diagnostic tests. Reference materials are valuable to support the development, assessment and calibration of these tests. The use of World Health Organization (WHO) International Standards (IS), the highest order calibrant, allows for the harmonisation of data reporting which assists performance evaluation. WHO IS for emerging virus molecular testing are usually made by inactivating the pathogen of interest and they undergo extensive evaluation in multi-laboratory collaborative studies. However, the development of such reference material for Lassa virus (LASV) is challenging due to the requirement for high containment level facilities to handle LASV. Further, the development of molecular tests for the detection of LASV RNA is confounded by the high sequence diversity amongst circulating lineages and a need to evaluate performance against them.MethodsTo circumvent this, we have developed a low containment alternative using chimeric lentiviral particles packaging the RNA of five prototype LASV lineages. These were evaluated alongside the whole inactivated virus (Josiah strain) by 18 laboratories, across 25 methods, as part of an International multi-lab collaborative study.ResultsThe data showed equivalent performance to the authentic virus in reducing interlaboratory variability; also, they highlighted the variability in detection across LASV lineages and supported the establishment of the chimeric particles as a WHO Reference Panel for Lassa virus RNA, alongside a WHO IS. This will greatly facilitate molecular test development and evaluation.DiscussionOverall, the strategy has the flexibility to be applied to a range of high priority viral families and can rapidly be implemented to expand to new viral sequences of high consequence which may impact molecular test performance. This represents an important pandemic preparedness initiative to support the response to the next outbreak, including Disease X.

Immunogenicity testing for anti-drug antibodies (ADA) is mandatory for regulatory approval of a biotherapeutic and can, in some instances, continue post-licensure. Typical examples are TNF inhibitors where biotherapeutic and ADA levels are relevant in clinical decision-making for optimal patient therapy. However, challenges with non-comparability of results due to plethora of bioanalytical techniques and the lack of standardization has hindered ADA monitoring in clinical practice. Two human anti-infliximab monoclonal antibodies (A, B) with defined characteristics were therefore lyophilized and assessed for suitability as a reference panel for ADA assays in an international study. Binding assays included the simple ELISA and common electrochemiluminescence (ECL) to the rare antigen binding test and lateral flow assays. For neutralisation, competitive ligand binding and reporter-gene assays were employed. Sample testing (e.g., antibodies, sera) showed differential reactivity depending on the assay and sample. Estimates for ADA levels using in-house standards varied substantially among assays/laboratories. In contrast, using antibody A for quantitating ADA levels reduced the interlaboratory variability and provided largely consistent estimates. The degree of harmonization was dependent on the assay, sample and the laboratory. Importantly, antibody A allowed ADA detection when missed using in-house standards. Recognition of sample B varied, possibly due to its fast dissociation. Overall, the panel comprising A (coded 19/234) and B (coded 19/232) was suitable and established by the WHO Expert Committee on Biological Standardization in October 2022 as the WHO international reference panel for infliximab ADA assays. Sample A (coded 19/234) with an arbitrarily assigned unitage of 50,000IU/ampoule for binding activity and 50,000 IU/ampoule for neutralising activity is intended as a ‘common standard’ for assay characterization and where possible for calibration of anti-infliximab preparations to facilitate comparison and harmonization of results across infliximab ADA assays. Sample B (19/232) with its unique characteristics and variable detection but no assigned unitage is intended for assessing the suitability of the assay for detecting ADAs with fast dissociation. It is anticipated that this panel would help towards selecting and characterizing suitable assays, benchmarking of in-house standards where feasible and in harmonizing ADA assays used in clinical practice for better patient outcome globally.

At present, quality control of diphtheria vaccines by both manufacturers and national control laboratories relies heavily on in vivo assays to confirm potency. As part of the VAC2VAC project we have developed a monoclonal antibody (mAb) enzyme-linked immunosorbent assay (ELISA) to measure the relative amount and quality of diphtheria toxoid (DTxd) in diphtheria-tetanus based vaccines and believe this test has the potential to play a key role in a control strategy no longer including an in vivo potency test. The mAb ELISA is highly specific, has good dilutional linearity, and is suitable for detecting DTxd in a range of different human vaccine products. We demonstrate the ability of the assay to discriminate between batches of different content and quality using vaccine batches that were prepared to contain differing amounts of DTxd or were altered by exposure to heat or oxidative stress. We also demonstrate successful transfer of the method to other laboratories and show that different diphtheria antigen materials may be able to serve as a reference antigen for local standardization of the method. The assay is ideally suited for incorporation into a consistency approach for routine diphtheria vaccine quality control testing and may be suitable to serve as the stability indicating test in replacement of the current in vivo potency test.

An international collaborative study was jointly organised by the World Health Organization (WHO) and the European Directorate for the Quality of Medicines & HealthCare (EDQM) to establish the WHO 3

Antigen identity, quantity and integrity are key factors to be evaluated as part of consistency testing of tetanus vaccines. Here we have developed a monoclonal antibody sandwich [LISA to measure the relative amount and quality of tetanus toxoid (TTxd) in human and animal tetanus vaccines. The [LISA is highly specific, has good dilutional linearity, and is suitable for detecting TTxd in a range of different products. We have demonstrated the ability of the assay to discriminate between batches of different content, using vaccine batches that had been prepared to contain differing amounts of TTxd, and of different quality, using samples of non-adjuvanted TTxd that had been exposed to sonication and final lot vaccines that had been exposed to heat or oxidative stress. We have also demonstrated successful transfer of the method to other laboratories and have shown that different tetanus antigen materials may be able to serve as a reference antigen for standardization of the method. The results show this test has the potential to play a key role in a control strategy no longer including an in vivo potency test. Plain language summary Tetanus vaccines help to protect against tetanus infection. Currently, animal tests are used to ensure the potency of such vaccines. Since these tests were first introduced, there have been improvements in non-animal technologies that can be used to ensure consistent production of potent vaccine batches. To demonstrate that a new batch of tetanus vaccine is consistent with a previous batch of known potency, the quality and amount of the component that stimulates the immune response upon vaccination must be assessed in comparison. We have developed an assay that can measure the quality of a range of different tetanus vaccine product types. The assay is very specific and reliable, and different laboratories obtained comparable results, showing that the assay is suited for routine use. Once validated by manufacturers and accepted by regulators, this assay will greatly reduce the number of animals needed for batch release of tetanus vaccines.

This publication describes the outcome of a project to develop a replacement European Pharmacopoeia (Ph. Eur.) Biological Reference Preparation (BRP) for Human tetanus immunoglobulin (TIg) as well as for the World Health Organization (WHO) International Standard (IS) for Tetanus Immunoglobulin, Human. Bulk TIg was kindly provided by a European manufacturer and was used to prepare the candidate standard. The candidate standard was freeze-dried and calibrated in an international collaborative study jointly co-ordinated by the Medicines & Healthcare products Regulatory Agency (MHRA) and the European Directorate for the Quality of Medicines & HealthCare (EDQM, Council of Europe). The results of this study show that there was good agreement between laboratories for the potency estimates obtained for the candidate standard relative to the current WHO IS/Ph. Eur. BRP. The study also demonstrated that the candidate standard is suitable for use in Ph. Eur. assays for potency testing of TIg products and there was good agreement in the potency estimates obtained using the different assay methods included in the study. Accelerated degradation studies performed at the MHRA over a period of 4 years suggest that the freeze-dried candidate standard will be very stable. The candidate standard was established as Ph. Eur. BRP for Human tetanus immunoglobulin, batch 2 with an assigned potency of 45 IU/ampoule. The same preparation was also adopted by the WHO Expert Committee on Biological Standardization (ECBS) to serve as the WHO 2nd IS for Tetanus Immunoglobulin, Human (13/240).

An international hybrid meeting held 21-22 June 2023 in Ottawa, Canada brought together regulators, scientists, and industry experts to discuss a set of principles and best practices in the development and implementation of standards. Although the use of international standards (ISs) and international units (IUs) has been an essential part of ensuring human and animal vaccine quality in the past decades, the types and uses of standards have expanded with technological advances in manufacture and testing of vaccines. The needs of stakeholders are evolving in response to the ever-increasing complexity, diversity, and number of vaccine products as well as increasing efforts to replace animal -based potency tests with in vitro assays that measure relevant quality attributes. As such, there must be a concomitant evolution in the design and implementation of both international and in-house standards. Concomitantly, greater harmonization of regulatory expectations must be achieved through collaboration with standard -setting organizations, national control laboratories and manufacturers. Stakeholders provided perspectives on challenges and several recommendations emerged as essential to advancing agreed upon objectives.

An international collaborative study was jointly organised by the World Health Organization (WHO) and the European Directorate for the Quality of Medicines & HealthCare (EDQM) to establish the WHO 3rd International Standard (IS) for Prekallikrein activator (PKA) and European Pharmacopoeia (Ph. Eur.) PKA in albumin Biological Reference Preparation (BRP) batch 7. Twenty-six laboratories took part in the study to calibrate these replacement batches, as well as an additional reserve batch for the WHO IS, against the current WHO 2nd IS for PKA (02/168). Ph. Eur. PKA in albumin BRP batch 6 was also included to evaluate the continuity of the consecutive batches of BRP. The centrally calculated overall Huber's means based on the results from laboratories with at least two valid assays were 29.6 and 29.6 IU/ampoule for the candidate WHO 3rd IS (Sample A) and reserve batch (Sample B), and were 38.4 and 37.0 IU/vial for the current BRP batch 6 (Sample C) and the candidate BRP batch 7 (Sample D). The intra-laboratory variation expressed as coefficient of variation (CV) ranged between 1.4 and 16.6 %. The inter-laboratory variation expressed as CV based on Huber's means ranged between 4.4 and 5.4 %. The Huber's mean activity of Sample D against Sample C was 36.6 IU/vial with a CV of 1.7 %. These results confirm the good continuity of the consecutive batches of BRP. Based on the results of this study, it is recommended to establish Sample A as the WHO 3rd IS for PKA with an assigned potency of 30 IU/ampoule and Sample D as the Ph. Eur. PKA in albumin BRP batch 7 with an assigned potency of 37 IU/vial. Sample B is intended to be kept as a future reserve replacement WHO IS.

Previously established World Health Organization (WHO) International Standards (IS) for anti-HPV16 and HPV18 antibodies are used to harmonize results across human papillomavirus (HPV) serology assays. Here, we present an international collaborative study to establish ISs for antibodies against HPV6 (NIBSC code 19/298), HPV11 (20/174), HPV31 (20/176), HPV33 (19/290), HPV45 (20/178), HPV52 (19/296) and HPV58 (19/300). The candidate standards were prepared using sera from naturally infected individuals. Each candidate was shown to be monospecific for reactivity against its indicated HPV type except for the HPV11 candidate, which was also reactive against other types. Expression of antibody levels relative to the relevant candidate IS reduced inter-laboratory variation allowing greater comparability between laboratories. Based on these results, the WHO Expert Committee on Biological Standardization established each of the 7 candidates as the 1st IS for antiserum to its indicated HPV type for use in the standardization of HPV pseudovirion-based neutralization and antibody-binding assays.

Three preparations of the human tumour necrosis factor (TNF) receptor II Fc fusion protein (TNFR II-Fc) Etanercept were formulated and lyophilised at the National Institute for Biological Standards & Control (NIBSC) prior to evaluation in a collaborative study for their suitability to serve as a World Health Organization (WHO) International Standard (IS)/European Pharmacopoeia (Ph. Eur.) Biological Reference Preparation (BRP) for the potency assay of Etanercept. Seven laboratories tested the preparations using an in vitro cell-based bioassay (TNF-α neutralisation) prescribed by the Ph. Eur. monograph on Etanercept (2895). The results of this study indicated that the candidate preparation, coded 13/204, established as the first IS for Etanercept with an assigned potency for TNF neutralisation activity of 10 000 IU per ampoule was also suitable to serve as Ph. Eur. BRP batch 1. The results were compared to those obtained with different cell-based neutralisation assays that were used by further laboratories in the context of establishing the 1st WHO IS for Etanercept. Based on these analyses, preparation 13/204 was adopted by the Ph. Eur. Commission as Etanercept BRP batch 1 with an assigned potency of 10 000 IU per ampoule.

For the batch release of vaccines, potency release assays are required. Non-animal in vitro tests have numerous advantages and are preferred; however, several vaccines are still released using in vivo assays. Their major drawback is the inherent variability with its practical implications. We quantified the variability of in vivo potency release assays for whole-cell pertussis, inactivated polio and meningococcal B (MenB) vaccines which showed large CV (Coefficient of Variation) ranging from 34% to 125%. As inherent variability might potentially be attributed to the highly variable immune system between individual animals, we evaluated the antibody titres to four MenB antigens in 344 individual outbred mice. These varied strongly, with more than 100-fold differences in antibody titres in responsive mice. Furthermore, within individual mice there was generally no correlation between the strengths of the responses to the four antigens. A mouse with a very low or no response to one antigen in many cases exhibited a strong response to another antigen. The large differences between individual animals is likely a considerable contributor to the inherent variability of in vivo potency assays. Our data again support the notion that it is preferred to move away from in vivo potency assays for monitoring batch to batch consistency as part of vaccine batch release testing.

Metrology - the science of measure - is a subject few biological scientists are taught about in their training to their detriment; the application of simple standardization processes to everyday working practices provides confidence in data and reproducibility over distance and time. This method demonstrates how to standardize a core laboratory experiment used widely in hemostasis research and clinical practice, specifically, measuring responses to the platelet collagen receptor (glycoprotein [GP]VI) agonist collagen-related peptide, cross-linked (CRP-XL) by light transmission aggregometry (LTA). Using this approach will ensure intra-lab reproducibility and inter-lab harmonization, regardless of agonist stock or supplier. Importantly, this method is applicable to other platelet agonists and, indeed, many other biological molecules and bioassays. The process outlined below involves making a 6-8 point dilution series of the 'standard' and the 'test' (the material you are checking) and running them side by side in a chosen assay (in this case, LTA). CRP-XL is used at mass/volume concentrations, but not every material gives the same biological activity at a given concentration, so a dilution series is made to compare the standard and test material and determine what concentration is needed to give equivalent activity. The dilution series must span 0-100% aggregation. Data is plotted using non-linear regression, and the EC50 value of each sample (standard and test) is determined. To assign activity, divide the EC50 value of the standard by that of the test to determine how much more or less potent it is and adjust the concentration accordingly. This approach will ensure that the same biological 'activity' is added to the assay time and time again.

Chromogenic assay discrepancies were reported at General European Official Medicines Control Laboratories Network (GEON) meetings by laboratories testing FVIII-products. The objectives of the present investigation were to carry out a controlled collaborative study to examine these reports and to delineate the reasons for these discrepancies by assessing affected and unaffected FVIII products. The laboratories followed a strict study protocol, which included assessing their own individual observed factor X (FX) activation times, i.e. the time to reach 50% of maximal FX activation (T1/2), for each chromogenic kit. This measurement was used, in parallel with the kit manufacturers' prescribed FX activation times, to assess the performance of the chromogenic potency assays on FVIII test products. This study confirmed a significant discrepancy between Coatest® and Coamatic® kits and between Siemens and Coamatic® kits when the kit manufacturers' prescribed T1/2 incubation times were followed. Coamatic® kits tended to produce higher potencies than the Coatest® or Siemens kits. Furthermore, FX activation assays revealed marked differences between individual laboratories for all three chromogenic kits in the observed T1/2 incubation times, which also did not correspond to the prescribed T1/2 incubation times. The resulting differences in potency between kits, in some cases, were significantly reduced when using the actual observed T1/2 incubation times instead of the prescribed T1/2 incubation times. The study showed that FVIII potency discrepancies can occur between chromogenic kits. To compensate for this, laboratories should ideally perform FX activation curves for each new chromogenic kit in order to determine the correct observed T1/2 incubation times, which can then be used to determine FVIII potencies in therapeutic concentrates.

Determination of the potency of a vaccine is critical to ensuring that an appropriate dose is delivered, lot-to-lot consistency is maintained, and that the formulation is stable over the life of the vaccine. The potency of inactivated influenza vaccines is determined routinely by the Single Radial Immunodiffusion (SRID) assay. A number of alternative potency assays have been proposed and have been under evaluation in recent years. The aim of this study was to compare a surface plasmon resonance-based assay and two different enzyme linked immunoassays against the current potency assay, SRID, and against mouse immunogenicity when haemagglutinin antigen of the A(H1N1)pdm09 component of an inactivated influenza vaccine is stressed by elevated temperature, low pH and freezing. This analysis demonstrated that the alternative assays had good correspondence with SRID for samples from most stress conditions and that the immunogenicity in mice corresponded with potency in SRID for all stress samples. Subject to further analysis, the assays have been shown to have the potential to possibly replace, and at least complement, SRID.